william w. weaver on sat 22 feb 97
I have been lurking in the corners of clayart and have thorughly enjoyed
reading my daily batch of clay messages. I have some questions etc. I would
appreciate some input on.
I have begun using terra sigg on my red earthenware body and while I have
\achieved good color the results of my labororious burnishing has been
somewhat disappointing. I have been using a terra sigg decanted from my
throwing bucket and applied over bone dry pieces followed by burnishing.
This process has not resulted a very high shine after firing. I do however
do get a very nice sheen. My questions are:
would use of redart clay ( just purchased 50lbs) produce a better shine?
I am firing in an oxidation environment ^04 bisque and ^06 glaze, would I
get a better shine with pit firing?
Are there any other tried and true techniques of making a terra sigg other
than Vince's elaborate decanting and siphoning process?
Is a defloculant needed and if so what seems to work best?
Thanks any and all feedback, comments or ???? would be appreciated.
Bill
Marcia Selsor on sun 23 feb 97
I use red art for terra sig and follow the Kenny recipe from the
Complete Book of Pottery (old). I bisque to ^012 and then sawdust fire
AKA pit fire, smoke fire, etc. If you bisque higher than ^012 you can
dull the sheen. I buff the TS with a soft cloth rather than stone or
spoon. To check the results look at my page in Artscape, 4th picture
bowl with reclining figure.
http://www.artscape.com
Marcia in Montana
--
Marcia Selsor
http://www.imt.net/~mjbmls/
mjbmls@imt.net
Vince Pitelka on mon 24 feb 97
>I am firing in an oxidation environment ^04 bisque and ^06 glaze, would I
>get a better shine with pit firing?
>Are there any other tried and true techniques of making a terra sigg other
>than Vince's elaborate decanting and siphoning process?
>Is a defloculant needed and if so what seems to work best?
Bill -
Hey . . . . you get what you pay for. Or in this case, what you WORK for.
If you want the very best sig for burnishing or polishing, then all the
trouble you go to to make my super-refined sig is absolutely worth it.
You do not say whether the initial burnish is satisfactory before firing.
If so, the problem is simply that you are firing too high. A terra sig
which has been polished with a soft cloth or brush can be fired up to ^04
without loosing its shine, but one which has truly been burnished with a
shiny stone or some other compressing tool will loose its burnish if fired
above about ^012.
Usually throwing water yields pretty good sig, because much of the grit and
coarser particles stay behind on the thrown wares. If you want to make good
sig you still have to settle and decant, and a deflocculant will help. It
is hard to measure the appropriate amount of defloc. when you are working
with an already liquid mixture. If you want to do this right, take the
scrap from your throwing bucket, and dry it out. Weigh it and then weigh
out 00.25% (thats 1/4 of one percent) EACH of sodium silicate and soda ash.
Don't know why it works better, but many people have had best luck using
both together. Add the defloc. to a small amount of hot water, and stir
until the soda ash is dissolved. Add the dry scrap from your throwing
bucket, and add more water as needed, letting it slake down. When slaked,
add water, stirring continuously, until the mixture is a thin milky
consistency. Let it sit overnight, and pour off the thinner portion on top.
This is your sig. Stop pouring when you get to thicker sediment. Of course
you can do exactly the same process using any dry clay, and the yield will
depend on the fraction of very fine particles in the clay. Redart give a
fairly high yield, ball clay gives an extremely high yield, kaolins and
fireclays give a lower yield.
In case you have not studied this, it is interesting to understand the
forces acting on the suspension and settling. You have three forces at work
here. First, you have ever-present atomic vibration, present in all things,
less so in solids, more so in liquids, more still in gases. In essence,
atomic vibration causes molecules to bounce off of one another. Second, you
have the electric or ionic charge of the particles. Adding a tiny amount of
an alkaline material as a deflocculant, lilke sodium silicate or soda ash,
causes the particles to have same electrical charges, which makes them repel
one another. Finally, you have gravitational force, which acts most
strongly on the larger particles. With a properly deflocculated slip,
atomic vibration and ionic charge are both working to keep particles in
suspension, while gravity is working to settle them out. The combination of
atomic vibration and ionic charge is powerful enough to keep particles
approximately one micron (1/1000 of a mm) or less in suspension, while
larger particles settle out. My research has shown that a settling period
of about 20 hours is ideal. Less than that and the larger particulates have
not settled adequately. More than that and even the smallest particles
might begin settling out.
Keep in mind that once you decant off the sig it will be way to thin to use.
Pour it out in any wide flat containers, like oil-drain pans, and let it
evaporate for a week or so. If you want the real thing, don't rush this,
and don't skip steps. Even the above is an abbreviated proceedure for
making sig without a hydrometer and without a siphon. I expect you will
waste some sig, and your results will not be consistent until you really get
a system down, but if you are determined not to measure s.g. or use a siphon
this should work pretty well.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
John Guerin on tue 25 feb 97
In a message dated 97-02-24 10:38:24 EST, you write:
<< You do not say whether the initial burnish is satisfactory before firing.
If so, the problem is simply that you are firing too high. A terra sig
which has been polished with a soft cloth or brush can be fired up to ^04
without loosing its shine, but one which has truly been burnished with a
shiny stone or some other compressing tool will loose its burnish if fired
above about ^012. >>
As Vince said, the firing process will reduce the burnished shine. The
microscopic thin platlettes of clay that you lined up on the surface of the
vessel through burnishing are what provides the reflective, shiney surface.
When the platlettes are vitrified, they curl slightly and loose some of their
shine. When I was studying with a Tewa Potter, he showed me an old Indian
trick to restore the shine. If you want that shiney surface back, apply a
coat of liquid floor wax to the surface of the vessel. When dry, buff with a
soft cloth. This only works on a burnished vessel where you've closed up the
pores of the clay. On an unburnished surface, the liquid wax just soaks in
and disappears.
John Guerin
Tucson,AZ
Chris Kunze on wed 26 feb 97
Why does a piece burnished with a cloth keep it's shine at ^04 and one
burnished with a stone looses it's shine when fired above ^012???
Vince Pitelka on thu 27 feb 97
At 11:48 AM 2/26/97 -0500, you wrote:
>----------------------------Original message----------------------------
>Why does a piece burnished with a cloth keep it's shine at ^04 and one
>burnished with a stone looses it's shine when fired above ^012???
>
As I understand it, clay which has been polished with a cloth or brush, but
which has not been compressed bt burnishing, can shrink a bit without
damaging the shine, thus the ability to be fired up to ^04 or even higher.
When clay is burnished with a smooth hard object, the platelates are all
forced down flat, and compressed together extremely closely, and any
shrinkage will disrupt this finish. If the piece shrinks at all, this
highly compressed burnished surface "buckles" on a microscopic level, which
matts the surface.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
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